Asthma is a common disease with allergy being the commonest cause. Those patients with the most severe form consume a disproportionately high share of the healthcare budget. Apart from common environmental allergens, sensitisation to a number of fungi including Aspergillus spp. is commonly found in many atopic individuals. Sensitisation to fungi is associated with increased asthma medication usage, asthma admissions due to exacerbations, intensive care admissions for asthma, respiratory arrest and even asthma deaths. A number of mechanisms have been proposed for the implication of fungi to induce an allergic response. These include the wide
spectrum of allergenic molecules released by fungi, especially those with inherent proteolytic activity. Volatile organic compounds have also been found to be responsible. Allergic bronchopulmonary aspergillosis (ABPA) is the archetypal allergic fungal disease whereby Aspergillus fumigatus colonises the airway in a sensitised individual, and is associated with the formation of Aspergillus-specific IgE and IgG. Severe asthma with fungal sensitivity (SAFS) describes a group of asthma patients with refractory asthma symptoms, sensitisation to one or more common fungi, but lacking the diagnostic criteria for ABPA (such as Aspergillus-specific IgG, proximal bronchiectasis in CT thorax etc.). The importance of this empirical categorization lies in the response to anti-fungal therapy.